1. Field of the Invention
The present invention relates to the field of fabrication equipment, and more particularly but not by way of limitation, to an improved linear press assembly having flexible manufacturing capabilities for processing sheet material.
2. Discussion
Soft-tooling methods of manufacturing,and more particularly that of processing sheet metal by punching and forming operations, are well known and widely used in the metal fabrication industry. Soft-tooling methods refer generally to manufacturing processes utilizing non-dedicated tooling. Conversely, hard-tooling methods generally involve processes utilizing tooling that is built for a particular part or grouping of similar parts. Although hard-tooling methods provide superior cycle-time efficiency because the press typically punches only one time for each part produced, the changeover time and inflexibility of hard-tooling limits its use to production schemes employing large batch sizes. Modern production demands for flexibility, just-in-time delivery, and near 100% utilization of all valve-added resources justify the use of soft-tooled manufacturing methods.
Computer numerically controlled (CNC) punch presses are commonly used in soft-tooling methods, wherein individual tools are used in designated punch hit and sheet material positioning schemes to produce a wide variety of different parts. CNC presses require only a fraction of the changeover time from one part to the next as compared to hard-tooled die methods. CNC presses furthermore offer savings in initial tool investment as the individual tools may be used in limitless combinations to produce a wide variety of different parts without dedicating any tooling to a particular part. Forming operations in addition to punching operations are common in CNC presses, where bullet punches and louver and embossment sections are commonly used to that end. Even when hard-tooling methods are used as the primary manufacturing method it is customary to have in place alternative soft-tooled methods as a backup.
CNC presses permit a minimal outlay in tooling expenditures because a fixed number of tools can be used to make any desired part. This is achieved by using a punch with multiple material repositionings to nibble uncommon features or profiles. Nibbling also reduces changeover time in the part production sequence by eliminating tool changeouts between parts.
Parts nesting, too, is a common practice which provides the ability to make different parts out of a common blank. Typically this is done where different parts are needed in downstream operations such as a subassembly operation. Shaker tabs are commonly formed between the parts so that the processed blank can be removed intact, and the parts can be easily separated thereafter. The diversity offered by CNC press technology provides the ability to pick and choose which parts to run together and typically involves a simple interaction between the operator and the press to download the individual part computer programs into a combined nested program.
Flexible manufacturing methods such as those of a CNC press best support a just-in-time manufacturing approach to scheduling production. CNC presses are more conducive to diverse varieties and short lot runs in comparison to large bed punch presses. The dynamics of flexibility and just-in-time scheduling have created an increased demand for soft-tooled manufacturing methods and will continue to drive the development of improvements in the art.
The prior art CNC presses typically employ a bridge-type frame supporting a sheet material delivery system in communication with a tool delivery system. The sheet material delivery system responds to programmed instructions to move the sheet material within a two-axis plane to deliver that portion to be processed to a punch location. Simultaneously, the tool delivery system delivers the selected punch and matingly aligned die to the punch location. A punching force is then delivered to drive the punch through (or against if forming) the sheet material which is supported by the die. Well known limitations of existing CNC presses include limited tool storage capacity, cumbersome tool change-outs, the expense of specialty tooling,and the inability to use more than one tool at a time.
The earliest solutions in the art are represented by the turret type punch press, as is taught in U.S. Pat. Nos. 3,449,991 and 3,717,061 issued to Daniels. The turret press uses a rotary turret to hold the tools. The turret responds to programmed instructions to rotate and position the selected tool relative to a punching head. One disadvantage of the turret press is the limited number of tools that can be stored in a turret, which ranges from about twenty to sixty tools. Another disadvantage of the turret press is that each individual punch and die must be maintained in alignment as the turret is rotated. Misalignment causes premature tool wear and sometimes catastrophic tool failure.
An alternative prior art approach is the cartridge type punch press, as is taught in U.S. Pat. No. 4,503,741 issued to Hunter. This cartridge press uses one or more pairs of mating cartridge tool holders. The cartridge pairs are moved to deliver the selected tool within a cartridge to the punching head. Although the cartridges offer improvements in tool delivery, disadvantages such as tool alignment problems and limited tool capacity are not resolved.
World class manufacturing methods and the business practices that drive them unquestionably will continue to emphasize maximizing part velocity through the manufacturing process. The era of building large in-process inventories has effectively been replaced by the practice of producing small batch quantities of in-process material and delivering them just-in-time for use. Cellular manufacturing approaches operating in accordance to regimented scheduling schemes provide the flexibility and part velocity meets today's demand for near 100% utilization of all value-added processing centers in an organization.
The demand for faster presses that are capable of more operations with larger tool holding capacities and of simpler mechanical design will foster revolutionary improvements in the field of material processing. There is a long-felt need in the industry for a press that provides the best of both worlds, the operating efficiency of hard-tooled methods with the flexibility of soft-tooled methods.